The present invention relates to a horseshoe of the type having a resilient intermediate layer disposed to fill out the interspace between rigid upper and lower horseshoe parts.
Horseshoes of the type with two parts and a resilient intermediate layer therebetween are well known in the art for use e.g. by horses at races and horse shows to provide improved shock-absorption at impact between the horseshoe and the substratum.
In general, prior art two-part horseshoes comprise a hoof contacting plate, a ground contacting plate and an elastic layer interposed between the plates. The ground contacting plate and, possibly, the elastic layer are provided with holes large enough for passage of the head of a nail, while the hoof contacting plate is provided with smaller holes. Thereby, the nail head may engage with the hoof contacting plate or the interposed elastic layer.
WO 99/65298 discloses a shock-absorbing horseshoe, in which a resilient intermediate layer completely fills out the interspace between the upper and lower parts, the lower part being shorter than the upper part. The intermediate layer is secured to the upper and lower parts by adhesion of the resilient material used for the intermediate layer. Connection of the horseshoe with the hoof by conventional nails is accomplished solely by the engagement of the nail heads with the resilient intermediate layer. The two parts of the horseshoe are kept together by a combination of a rigid mechanical connection at the front of the horseshoe and the adhesive provided by from the resilient intermediate layer.
Danish patent No. 19,298 discloses a two-part horseshoe in which rear edges of the upper part are connected with the rear edges of the lower part by bolts. The bolt includes a head extending outside the horseshoe and functioning as a take-off. The bolt has a thread engaged with the lower part and passes through a knob of resilient material between the two parts into a hole in the upper part without being connected to the latter. Because of the lack of mechanical connection with the upper part the bolt may move freely up and down inside the hole in the upper part.
Whereas the construction of these two prior art horseshoes provides for a shock-absorbing effect, both have the disadvantage that the lower part is secured to the upper part solely by the mechanical connection at the front edge of the horseshoe and, in the case of the horseshoe disclosed in WO99/65298, partly by the adhesion of the resilient intermediate layer to the upper and lower parts. Due to the deflection of the two parts in use of the horseshoe, the front edge is subject to wear, resulting ultimately in destruction of the horseshoe by fracture and separation of the two parts.
This problem becomes even more pronounced with use of a soft and thus more comfortable material for the intermediate layer, because a softer material will require a more rigid mechanical connection at the front edge of the horseshoe when subjected to stress. In result, fatigue may occur in that part of the horseshoe and ultimately the lower part of the horseshoe may break off.
As evident from Danish patent specification No. 19,284 use of a further connecting means such as bolts to keep the upper an lower parts together may entail the problem that during use of the horseshoe such bolts may enter into the hoof of the horse and cause significant pain.
The same problem occurs with a horseshoe design disclosed in U.S. Pat. No. 918,094. This prior art horseshoe comprises a one-piece member provided with detachable plates and an interposed rubber filling near the rear ends of the horseshoe branches. The detachable plates and the rubber filling are held in place by engagement between lugs and openings in the lower part and the detachable plates and are further connected by a screw having a head engaged with the one-piece part and passing through the rubber filling for engagement with a thread in the detachable plate. Like the bolts used in Danish patent No. 19,284 this screw head may penetrate into the hoof and cause pain to the horse.
On the background of the state of the art as described it is the object of the invention to further improve the integrity of a horseshoe of the type defined without causing discomfort or pain to the horse.
In accordance with a first aspect of the present invention an improved horseshoe is provided, having a front edge and comprising a rigid upper part for engagement with the lower side of the hoof of the horse and a rigid lower part mechanically connected with the upper part at said front edge, the lower part extending at least under a part of the upper part, said upper and lower parts forming horseshoe branches each providing a rear edge, and a resilient intermediate layer positioned to fill out the interspace between the upper and lower parts, wherein the improvement comprises interlocking means for interconnection of the upper and lower parts adjacent to at least one of the rear edges of the branches of the lower part to prevent separation of the upper and lower parts, while allowing elastic deformation of the resilient intermediate layer.
Thereby, the upper and lower horse shoe parts become safely interlocked and thus prevented from falling apart, while still maintaining the intended functionality of the resilient intermediate layer with respect to improved dampening at impact of the horse hoof against the substratum, stable engagement with the substratum at take-off of the hoof and safe securing with respect to the hoof.
In addition, the horseshoe according to the invention provides a simple construction enabling manufacture at a competitive price.
Preferably the interlocking means is loosely connected with the upper part and rigidly connected with the lower part.
This is advantageous in two ways. Firstly the interlocking means does not prevent the resilient compression of the intermediate layer between the two parts during use. Secondly, the interlocking means is held securely inside the horseshoe by the rigid mechanical connection to the lower part.
In one embodiment said interlocking means extends through a hole formed in the upper part. In another embodiment an upper surface of the interlocking means is separated from an upper surface of the upper part to provide a clearance between said upper surfaces. Preferably, this clearance is filled out with resilient material.
The latter embodiment is advantageous by providing a xe2x80x9ccushionxe2x80x9d in the clearance between the head of the interlocking means and the hoof of the horse. When the intermediate resilient layer is compressed during use, whereby the head is pressed upwards towards the underside of the hoof this cushion will prevent the head of the interlocking means from penetrating into the hoof.
In one embodiment, the resilient material filled nto the clearance is the same as the material constituting the resilient intermediate layer.
Thereby, the cushion may be formed in said clearance in the same single process as the filling of material to form the resilient intermediate layer.
In one embodiment, the resilient intermediate layer consists of a moulded resilient plastic material, preferably polyurethane.
Resilient plastics and rubbers have good working properties and may by moulding be brought to adhere well to the surfaces of the upper and lower parts. In particular, polyurethane (P) has turned out to be a suitable material as tests have demonstrated it to be a well performing resilient and durable material.
In one embodiment, a low-cost and simple interlocking means is provided by a rivet- or screw-like member rigidly secured in the lower part and having a substantially flat head adapted to be positioned in said hole.
In accordance with a second aspect of the present invention, there is provided a method for manufacturing a horseshoe having a front edge and comprising a rigid upper part for engagement with the lower side of the hoof of the horse and a rigid lower part mechanically connected with the upper part at said front edge, the lower part extending at least under a part of the upper part, said upper and lower parts forming horseshoe branches each providing a rear edge, a resilient intermediate layer positioned to fill out the interspace between the upper and lower parts, and interlocking means for interconnection of the upper and lower parts adjacent to at least one of the rear edges of the branches of the lower part to prevent separation of the upper and lower parts, while allowing elastic deformation of the resilient intermediate layer according to any of the preceding claims, said method comprising the steps of:
cutting or punching said upper and lower parts from sheet material, preferably steel sheet;
disposing said upper and lower parts to extend substantially parallel to each other with an interspace therebetween;
disposing said interlocking means to interconnect the upper and lower parts near at least one of the rear edges of the branches of the lower part to prevent separation of the upper and lower parts, while allowing elastic deformation of the resilient intermediate layer; and
embedding resilient material into the interspace between the upper and lower parts to form said resilient intermediate layer.
In a preferred implementation of this method at least one hole is formed at a position in the upper part in alignment with a position near the rear edges of the branches of the lower part and said interlocking means is arranged in said hole with an upper surface of the interlocking means separated from an upper surface of the upper part to provide a volume between said upper surfaces; and said resilient material is embedded to fill out said volume.
The upper and lower horse shoe parts may be made from any suitable material having the required rigidity and wearability, but typically a metal with good wearability and good working properties like for instance steel is chosen.